The present invention relates to a valve for a motor vehicle fuel tank.
The invention relates more particularly to a valve for connecting to a degassing circuit, firstly to enable the air contained in the tank to be evacuated while the tank is being filled, and secondly to allow the tank to breathe.
The degassing circuit generally communicates with the atmosphere via an activated carbon filter, also known as a xe2x80x9ccannisterxe2x80x9d, that is intended to prevent fuel vapor being rejected into the atmosphere.
It is desirable to prevent droplets of fuel being entrained into the degassing circuit and reaching the cannister while the vehicle is running since that would rapidly saturate the cannister and cause it to lose its effectiveness.
The present invention provides a novel valve capable simultaneously of allowing the tank to be ventilated effectively during filling, of avoiding overfilling, and of subsequently allowing the tank to breathe, while also reducing the risk of liquid fuel reaching the degassing circuit while the vehicle is running.
The valve of the invention is for connection to a degassing circuit defining a passage for the flow of gas leaving the tank, and the valve comprising at least one moving member capable of being controlled in displacement to modify the configuration of the valve, and a first moving valve element including an orifice and suitable for being driven in displacement by the moving member from a first position towards a second position, changeover from the first position to the second reducing the flow section available to the flow of gas.
By means of the invention, the valve can be configured in such a manner that tank ventilation takes place either with gas flow at a high rate during filling, or else at a low rate with small risk of liquid fuel being splashed towards the cannister, particularly while the vehicle is running.
In a particular embodiment, the configuration of the valve is modified by the energy of a fuel pump, which is advantageously the same as the pump that is used for delivering fuel to the injectors of the engine.
The valve is advantageously arranged in such a manner that said moving member can be entrained to move under the effect of the fuel pump operating.
In a particular embodiment, the valve is arranged so that the moving member is entrained to move from the first position towards the second position under the effect of a variation in pressure created by the pump operating.
Advantageously, said variation in pressure is suction created by the Venturi effect.
In particular embodiment, the valve has a second closure element suitable for closing the orifice of the first closure element.
This second closure element advantageously closes said orifice in the event of the vehicle accidentally rolling over.
In a particular embodiment, the second closure element has positive buoyancy so as to close said orifice under the effect of a wave of fuel sloshing in the tank.
In a particular embodiment, the first closure element bears against a fixed seat when in its second position.
In another particular embodiment, the valve has an element forming a moving seat, and the first closure element bears against it when it is in its second position providing partial closure.
This seat-forming element is advantageously movable between a position in which it comes into abutment against said moving member and a position in which it is engaged on a rim of a fixed portion of the valve.
In a particular embodiment, the first closure element presents positive buoyancy, the valve being further arranged so that the first closure element takes up its partial closure position under the effect of liquid fuel rising in the tank at the end of filling.
In a particular embodiment, the first closure element needs to be moved upwards to go from the first position to the second position.
In a particular embodiment, the valve comprises:
a member that is movable along a substantially vertical axis from a low position while the tank is being filled and the engine is switched off to a high position while the engine is running;
a seat-forming element that is movable between a low position in which it is hooked on a fixed portion of the valve and supports the moving member, and a high position in which it comes into abutment against said fixed portion;
a first closure element presenting an orifice and that is movable when the moving member is in its low position between a first position in which it is spaced apart from seat-forming element and a second position in which it bears against said seat-forming element and reduces the flow section available to the flow of gas leaving the valve, allowing the flow to take place through said orifice only, said first closure element presenting positive buoyancy so as to go from its first position towards its second position under the effect of the fuel rising in the tank;
a second closure element that is movable relative to the first closure element between a first position in which its weight acts on the first closure element and a second position in which it closes said orifice, said second closure element presenting positive buoyancy so as go from its first position towards its second position under the effect of the liquid fuel rising in the tank and close the valve when the tank is at the end of filling and the engine is switched off, the moving member then being in its low position;
in which valve, once the engine is running, the moving member is in its high position and has entrained the seat-forming element into a high position with the first closure element held to bear against the seat-forming element by said moving member, the orifice of the first closure element then being normally open in the absence of waves of fuel in the tank, and the second closure element being suitable for closing said orifice under the effect of a wave of fuel in the tank.
The invention also provides a motor vehicle fuel tank fitted with a valve as specified above.